GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 12-13
Presentation Time: 11:15 AM


SHOWERS, William, Dept. of Marine, Earth, and Atmospheric Sciences, North Carolina State University, 2800 Faucette Dr, Raleigh, NC 27695,

Sustainable agricultural practices are crucial for protecting water quality as the demand for global food doubles over the next 50 years. Yet the transport of nutrients over landscapes and into aquatic ecosystems is poorly understood. The new generation of optical instruments can be used to map water quality parameters on a watershed scale with mobile and fixed platforms. The 15 year record on the NC Coastal Plain demonstrates that there are inter-annual flux variations associated with El Nino oscillations modified by the North Atlantic oscillation. Positive ONI and NAO indexes are associated with increased groundwater levels, higher nutrient fluxes, and estuary fish kills. Significant diurnal variation has also been observed in nitrate concentrations during high and low flow periods associated with waste water treatment plants. This long term chemical sensor network has demonstrated that chemical variability in aquatic environments are chronically under-sampled and has led to underestimating the nutrient flux from urban and rural watersheds.

Spatial mapping of watersheds indicates that nitrate, Chlorophyll a, and CDOM are not spatially coherent and one concentration cannot be used to predict the distribution of the other parameters as suggested by some regulatory agencies. Downstream nitrate concentration variations are not related specifically to buffer conditions adjacent only to the main stem river system, but to the conditions of all the tributaries and main stem river buffers in the entire drainage. Changes in riverine nitrate concentrations are related to the % of cultivated or pastureland located within the 100 foot river buffer area that is underlain by partially hydric or non-hydric soils. These “CRITICAL BUFFER” areas are prone to “leak” contaminates into the river ecosystems. Hysteresis loops of sediment and nutrient concentrations during large storm events indicate that surface runoff dominates storm hydrographs where critical buffers are abundant, and groundwater inputs dominate storm hydrographs in areas where critical buffers are less than 10% of the river buffer area. Agricultural cost share programs should focus on improvements in these critical buffer areas to protect future water quality.